The present invention also relates to a method of optimising an existing WDM transmission system with at least one transmitter and at least one receiver connected by means of a dispersive transmission line for operation at a higher bit rate.
Furthermore, the present invention relates to a computer program product for use in a WDM transmission system with at least one transmitter operatively connected with a transmitter-side Tuneable Dispersion Compensation Module (TDCM) and at least one receiver operatively connected with a receiver-side TDCM, and with at least one data processing means adapted to control dispersion compensation values of said TDCMs.
Optical Wavelength Division Multiplex (WDM) transmission systems are highly impaired by the combined effects of dispersion and Kerr non-linearities. In this context, dispersion management is usually employed to mitigate such impairments. Dispersion management involves placing Dispersion Compensation Modules (DCM) along the transmission line in order to control total cumulated dispersion as well as dispersion compensation distribution, which has an impact on non-linear impairments.
Nowadays, optical WDM transmission systems operating at 2,5 and 10 Gbit/s are widely used. However, in the near future 40 Gbit/s systems and/or systems operating at even higher bit rates are about to be deployed. The corresponding issue of system migration to higher bit rates particularly involves dispersion management, the constraints of which are rather tight at bit rates of 40+ Gbit/s. Furthermore, system migration to higher bit rates generally requires modified dispersion management solutions, since a dispersion map optimised for 10 Gbit/s generally will not be compatible with 40 Gbit/s even though total cumulated dispersion is well adjusted. In addition, inline trade-offs, such as pre-compensation, inline compensation or the like, also change in connection with system migration.
When designing a new, so-called “green field” high bit rate system, e.g. for operation at 40 Gbit/s, one can design a specific dispersion map for said system and use tuneable DCMs (Tuneable Dispersion Compensation Module—TDCM) and/or electronic compensation devices to adjust cumulated dispersion at system installation and live system fluctuations due to temperature effects during operation.
When migrating a low bit rate system to higher bit rates, it is known to add system complexity at both transmitter and receiver side to generate adapted advanced modulation formats that can be operated while preserving the dispersion map originally designed for the lower bit rate. However, this is possible only if the transmission length is not too long. Furthermore, the use of complex modulation formats adapted to the transmission line by means of electrical/optical devices has proved very costly.